After installing a personal certificate issued by a web service and enabling "Use third-party CA" in secret settings, if it's not working, first ensure correct certificate installation and verify the entire certificate chain. Double-check application-specific settings, confirm compatibility, and restart your device. Make sure the certificate is trusted by the application or service, and consult their documentation for any specific requirements.

Hmm, it looks like you are confusing certificate authority certificates with personal certificates. Yes that way CA CERTs work, but no that way personal CERTs (with secret keys) not work.